/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.zookeeper.server.quorum;

import java.io.IOException;
import java.util.concurrent.LinkedBlockingQueue;

import org.apache.zookeeper.KeeperException.Code;
import org.apache.zookeeper.ZooDefs.OpCode;
import org.apache.zookeeper.proto.ReplyHeader;
import org.apache.zookeeper.server.Request;
import org.apache.zookeeper.server.RequestProcessor;
import org.apache.zookeeper.server.ZooKeeperServer;
import org.apache.zookeeper.server.ZooTrace;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * This processor is at the beginning of the ReadOnlyZooKeeperServer's
 * processors chain. All it does is, it passes read-only operations (e.g.
 * OpCode.getData, OpCode.exists) through to the next processor, but drops
 * state-changing operations (e.g. OpCode.create, OpCode.setData).
 */
public class ReadOnlyRequestProcessor extends Thread implements RequestProcessor {

	private static final Logger LOG = LoggerFactory.getLogger(ReadOnlyRequestProcessor.class);

	private boolean finished = false;

	private RequestProcessor nextProcessor;

	private LinkedBlockingQueue<Request> queuedRequests = new LinkedBlockingQueue<Request>();

	private ZooKeeperServer zks;

	public ReadOnlyRequestProcessor(ZooKeeperServer zks, RequestProcessor nextProcessor) {
		super("ReadOnlyRequestProcessor:" + zks.getServerId());
		this.zks = zks;
		this.nextProcessor = nextProcessor;
	}

	@Override
	public void processRequest(Request request) {
		if (!finished) {
			queuedRequests.add(request);
		}
	}

	public void run() {
		try {
			while (!finished) {
				Request request = queuedRequests.take();

				// log request
				long traceMask = ZooTrace.CLIENT_REQUEST_TRACE_MASK;
				if (request.type == OpCode.ping) {
					traceMask = ZooTrace.CLIENT_PING_TRACE_MASK;
				}
				if (LOG.isTraceEnabled()) {
					ZooTrace.logRequest(LOG, traceMask, 'R', request, "");
				}
				if (Request.requestOfDeath == request) {
					break;
				}

				// filter read requests
				switch (request.type) {
				case OpCode.sync:
				case OpCode.create:
				case OpCode.delete:
				case OpCode.setData:
				case OpCode.setACL:

					ReplyHeader hdr = new ReplyHeader(request.cxid, zks.getZKDatabase().getDataTreeLastProcessedZxid(),
							Code.NOTREADONLY.intValue());
					try {
						request.cnxn.sendResponse(hdr, null, null);
					} catch (IOException e) {
						LOG.error("IO exception while sending response", e);
					}
					continue;
				}

				// proceed to the next processor
				if (nextProcessor != null) {
					nextProcessor.processRequest(request);
				}
			}
		} catch (InterruptedException e) {
			LOG.error("Unexpected interruption", e);
		}
		LOG.info("ReadOnlyRequestProcessor exited loop!");
	}

	@Override
	public void shutdown() {
		finished = true;
		queuedRequests.clear();
		queuedRequests.add(Request.requestOfDeath);
		nextProcessor.shutdown();
	}

}
